This invention relates to a photomask on which a master pattern of patterns has been formed which are to be transferred (projected) onto substrates in lithographic processes for producing devices such as semiconductor integrated circuits, imaging devices (such as CCD), liquid-crystal display devices or thin-film magnetic heads.
In the fabrication of devices such as semiconductor integrated circuits, a transfer method is used in which, using a photomask having a master pattern of a circuit pattern to be formed, having been magnified, e.g., about four to five times, the pattern of this photomask is reduction-projected on an exposure-target substrate such as a wafer or a glass plate via a reduction projection optical system. What is used when the pattern of such a photomask is transferred is the projection exposure apparatus. Photomasks used in reduction projection type exposure apparatus of a step-and-repeat system or a step-and-scan system are also called reticles.
In the transfer of the pattern of such a photomask, where any foreign matter such as dust with a size larger than tolerance limits stands adherent to the pattern surface, an image of the foreign matter may also inevitably be transferred to the substrate such as a wafer, and there is a possibility that integrated circuits finally manufactured may function erroneously. Accordingly, a thin film called a pellicle which is comprised of an organic material of about 1 to 10 xcexcm thick and transmits exposure light is conventionally spreadingly provided at a position about 5 mm apart from the photomask pattern surface so that the pellicle can prevent the foreign matter from adhering to the pattern surface. Also, the pellicle is spread over a metallic support frame called a pellicle frame bonded to the photomask pattern surface, and the space between the photomask pattern surface and the pellicle is substantially isolated from the open air and is so constructed that any foreign matter contained in the open air does not adhere to the photomask pattern surface.
As stated above, the pellicle comprised of a thin film of an organic material is spread over the pattern surface of any conventional photomask and this pellicle prevents dust from adhering. Also, as exposure light of projection exposure apparatus making use of photomasks, i-rays (wavelength: 365 nm) of mercury lamps have chiefly be used in conventional apparatus, where even conventional pellicles have a sufficient durability against exposure light having a wavelength of such a level.
On the other hand, exposure wavelengths of projection exposure apparatus are recently being replaced with much shorter wavelengths in order to make adaptation to semiconductor integrated circuits having been made finer, and recently KrF excimer laser light (wavelength: 248) is becoming prevailing. Then, at present, shorter-wavelength ArF excimer laser light (wavelength: 193 nm) is being on the stage of practical use. A projection exposure apparatus making use of much shorter-wavelength F2 laser light (wavelength: 157 nm) is also on research.
As exposure wavelengths are replaced with such shorter wavelengths, it has become difficult for conventional organic type pellicles to ensure a sufficient durability. More specifically, since exposure light having a shorter wavelength has a higher energy per one photon, chemical bonds of organic molecules constituting a pellicle may be broken by exposure light. Hence, it is becoming difficult to provide a pellicle comprised of an organic material sufficiently durable to short-wavelength exposure light.
However, if the pellicle is not used, the foreign matter can not be prevented from adhering to the photomask pattern surface, bringing about a difficulty that the manufacture of semiconductor integrated circuits results in a low yield.
Accordingly, it is desirable that any substance other than the pellicle comprised of an organic material be installed in the vicinity of the position where the pellicle has conventionally been provided. Conventional pellicles are workable in very thin gage and moreover soft, and hence any optical influence is almost negligible as long as deflection is removed by applying a tension. However, almost no substance is known which has the same nature as conventional pellicles in respect of exposure light of 200 nm shorter and yet can ensure transmittance.
In the case when the exposure light of 200 nm or shorter is used, it is also known that impurities such as moisture and organic matter present there may contaminate light transmission surface or cause a decrease in transmittance through space. Accordingly, the greatest possible care must also be taken for contamination of any light transmission surface of an article corresponding to the pellicle provided at the position set on the same optical path of the pellicle.
In addition, as disclosed in WO99/49366, it is proposed to use a transmitting plate in place of conventional pellicles as a countermeasure for the trend toward shorter wavelength of exposure light. However, some problems may arise when such a transmitting plate is used. First, the transmitting plate has a considerable thickness compared with the pellicle, and hence it is necessary to measure a figure tolerance (surface precision) on the pellicle side and the projection lens side. However, in the measurement of the figure tolerance (surface precision), where the both surfaces are flat and substantially in parallel, fringes of equal-thickness interference occur when light is made incident on the surfaces. An influence of such fringes of equal-thickness interference provides a problem that it is difficult to analyze interference fringes for measuring the figure tolerance (surface precision).
There is also a problem that aberrations may occur since the transmitting plate having a thickness is inserted in the optical path to any reduction projection optical system in which various aberrations have been well corrected in the state where any transmitting plate is not present. To cope with this problem, as disclosed in WO99/49366, a method is proposed in which the space between lenses of a reduction projection optical system is adjusted according to the thickness of the transmitting plate. This method may be easy and effective because any lens component may be moved in a relatively small extent when, e.g., the error (aberration) is regulated in the state the transmitting plate has a thickness set previously. However, where a plurality of reticles having transmitting plates in various thickness are used, the lens component must be moved in so large an extent that there is a possibility of exceeding the stroke of adjustment which is the range within which the lens is movable. Also, even if it is moved within the adjustable range, residual aberrations may occur.
Moreover, in the case when the transmitting plate is inserted to the optical system, it is preferable for the transmitting plate not to lower the transmittance as far as possible, i.e., to be low reflective. In addition, it is preferable to cause flare or the like as less as possible.
The present invention was made taking account of the problems discussed above. Accordingly, an object of the present invention is to provide a photomask which has a sufficient durability to short-wavelength exposure beams, too, and also can prevent any foreign matter from adhering to patterns for transfer.
Another object of the present invention is to provide a photomask which is a photomask having a transmitting plate and in which the figure tolerance (surface precision) of the transmitting plate can be measured with ease and also the transmitting plate is low reflective, and to provide a photomask, and a projection exposure apparatus, which can make aberrations less occur even when the transmitting plate has a variety in thickness.
To achieve the above objects, first invention provides a photomask on which a transfer pattern to be transferred to an exposure-target substrate is formed and through which a stated exposure beam applied to a pattern surface where the transfer pattern is formed is guided to a projection optical system for forming an image of the pattern;
the photomask comprising a transmitting plate disposed apart from the pattern surface by a stated interval and having a stated thickness and a transmission to the exposure beam;
the transmitting plate being substantially square and fulfilling the following condition:                     h        ≥                              60                                          "LeftBracketingBar"                β                "RightBracketingBar"                            ⁢              λ                                ⁢                      xe2x80x83                    ⁢                                    n              -              1                        n                    ⁢          0.0013          ⁢                      xe2x80x83                    ⁢                      ρ            F                    ⁢                      a            3                                              (        1        )            
where;
h: thickness (cm) of the transmitting plate;
n: refractive index of the transmitting plate with respect to the exposure beam;
xcex2: magnification of the projection optical system;
xcex: wavelength (cm) of the exposure beam; and
xcfx81: density (g/cm3) of the transmitting plate; and where Young""s modulus is represented by E and Poisson""s ratio is represented by "sgr",
E=E/(12xc2x7(1xe2x88x92"sgr"2))xe2x80x83xe2x80x83(2).
Second invention is that, in the 1st invention, the photomask may preferably fulfill at least one condition of the following conditions (a) to (c).
|xcex94T|xe2x89xa60.1xcex,xe2x80x83xe2x80x83(a)
xe2x80x83|xcex94"PHgr"|xe2x89xa60.1xcex,xe2x80x83xe2x80x83(b)
|xcex94n|xc3x97hxe2x89xa60.1xcex,xe2x80x83xe2x80x83(c)
where;
xcex: wavelength (cm) of the exposure beam;
xcex94T: difference (cm) in thickness of the transmitting plate between its maximum value and its minimum value;
xcex94"PHgr": difference (cm) in isophase plane of plane waves between its maximum value and its minimum value; the plane waves having passed through the transmitting plate when plane waves are made incident on the transmitting plate;
xcex94n: difference in refractive index of the transmitting plate with respect to the exposure beam, between its maximum value and its minimum value; and
h: thickness (cm) of the transmitting plate.
Third invention is that, in a photomask which has a pattern surface where a pattern for transfer has been formed, and is to be irradiated by a stated exposure beam;
the photomask comprises a transmitting plate disposed apart from the pattern surface by a stated interval; and
the transmitting plate fulfills at least one condition of the above conditions (a) to (c).
Fourth invention is that, in the 1st invention to 3rd invention, the photomask may preferably fulfill the following condition.                     A         less than                                             1              5                        ⁢                          d              o                        ⁢            tan            ⁢                          xe2x80x83                        ⁢                          (                                                sin                                      -                    1                                                  ⁢                                  NA                                      "LeftBracketingBar"                    β                    "RightBracketingBar"                                                              )                                +                                    1              10                        ⁢            d            ⁢                          xe2x80x83                        ⁢            tan            ⁢                          xe2x80x83                        ⁢                          (                                                sin                                      -                    1                                                  ⁢                                  NA                                                            "LeftBracketingBar"                      β                      "RightBracketingBar"                                        ⁢                    n                                                              )                                                          (        13        )            
where;
A: size (cm) of a defect the transmitting plate has;
d0: distance (cm) between the pattern surface and the transmitting plate;
NA: numerical aperture on the image side of the projection optical system;
xcex2: magnification of the projection optical system;
d: thickness (cm) of the transmitting plate; and
n: refractive index of the transmitting plate with respect to the exposure beam.
Fifth invention is a photomask on which a transfer pattern to be transferred to an exposure-target substrate is formed and through which a stated exposure beam applied to a pattern surface where the transfer pattern is formed is guided to a projection optical system for forming an image of the pattern;
the photomask comprising a transmitting plate disposed apart from the pattern surface by a stated interval;
the transmitting plate fulfilling the above condition (13).
Sixth invention provides an exposure process comprising the steps of;
exposing the photomask according to any one of the first invention to third invention, to exposure light of 200 nm or shorter wavelength; and
transferring the pattern formed on the photomask, onto a photosensitive substrate in accordance with the exposure light.
Seventh invention is that, in the 1st invention, the transmitting plate may preferably be simple-supported and fulfill the condition of:                     h        ≥                              60                                          "LeftBracketingBar"                β                "RightBracketingBar"                            ⁢              λ                                ⁢                      xe2x80x83                    ⁢                                    n              -              1                        n                    ⁢          0.0041          ⁢                      xe2x80x83                    ⁢                      ρ            F                    ⁢                      a            3                                              (        3        )            
In eighth invention, in the photomask according to the first invention, the transmitting plate may preferably be peripheral-supported.
In ninth invention, in the photomask according to the 1st, 2nd, 3rd, 5th, 6th, 7th or 8th invention, the exposure beam may preferably be polarized light, and the transmitting plate may preferably have a distortion of 0.1xcex or below.
In tenth invention, in the photomask according to the 1st, 2nd, 3rd, 5th, 6th, 7th, 8th or 9th invention, the transmitting plate may preferably be bonded in the state of optical contact at a position outside the region where the pattern has been formed.
Eleventh invention is a process for producing a photomask on which a transfer pattern for transfer is formed and which is to be irradiated by a stated exposure beam; the process comprising;
a first step of preparing a transmitting plate having transmission to the exposure beam;
a second step of forming on the photomask a pattern for transfer;
a third step of measuring the distortion of the pattern;
a fourth step of calculating the figure (surface form) of the transmitting plate which figure (surface form) may substantially cancel the distortion component;
a fifth step of working the photomask so as to provide the figure (surface form) calculated in the fourth step; and
a sixth step of attaching the transmitting plate to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed.
Twelfth invention is a process for producing a photomask to be mounted on a projection exposure apparatus with which a pattern for transfer is projection-exposed onto a photosensitive substrate via a projection optical system; the process comprising;
a first step of preparing a transmitting plate having transmission to the exposure beam;
a second step of forming on the photomask a pattern for transfer;
a third step of calculating a distortion component in accordance with the light coming from the pattern via the transmitting plate and the projection optical system,
a fourth step of calculating the figure (surface form) of the transmitting plate which figure (surface form) may substantially cancel the distortion component;
a fifth step of working the transmitting plate prepared in the first step, so as to provide the figure (surface form) calculated in the fourth step; and
a sixth step of attaching the transmitting plate worked in the fifth step, to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed.
Thirteenth invention provides a photomask on which a pattern for transfer has been formed and which is to be irradiated by a stated exposure beam;
the photomask comprising a transmitting plate disposed apart by a stated interval from the pattern surface where the pattern has been formed and having transmission to the exposure beam;
the transmitting plate having a stated thickness and has a first surface and a second surface through each of which the exposure beam is to be made to pass;
the first surface and second surface being substantially plane surfaces, or curved surfaces having a stated refracting power, and;
where the angle formed by the first surface and the second surface is represented by xcex8 (unit: degree), the refracting power of the first surface by xcfx861 (unit: 1/mm), and the refracting power of the second surface by xcfx862 (unit: 1/mm);
fulfilling at least one condition of two conditions:
12.4xe2x80x3xe2x89xa6xcex8 less than 3xe2x80x2xe2x80x83xe2x80x83(20),
xe2x88x921/6,940 less than xcfx861+xcfx862xe2x89xa61/5,000xe2x80x83xe2x80x83(21).
Incidentally, when the condition (21) is fulfilled, any one of xcfx861xe2x89xa00 and xcfx862xe2x89xa00 is fulfilled.
The conditions (20) and (21) defines conditions for making the fringes of equal-thickness interference less occur and making the measurement of figure tolerance (surface precision) easy. When these conditions are not fulfilled, the fringes of equal-thickness interference may occur greatly and the measurement of figure tolerance (surface precision) may result in a low precision. When at least anyone of the conditions (20) and (21) is fulfilled, decentration aberrations may occur at a very low level or at a level of being correctable with ease.
Fourteenth invention provides a projection exposure apparatus in which a pattern for transfer which has been formed on the pattern surface of a photomask is illuminated by an exposure beam coming from an illumination optical system and an image of the pattern is formed on a photosensitive substrate via a projection optical system; the projection exposure apparatus comprising;
a mask stage for positioning the photomask in the optical path extending between the illumination optical system and the projection optical system; and
a mask stage drive for moving the mask stage so that the interval between the pattern surface and the projection optical system comes to be at a given value;
the photomask having a transmitting plate having transmission to the exposure beam, disposed apart from the pattern surface by a stated interval; and
the given value being determined in accordance with the thickness of the transmitting plate of the photomask.
Fifteenth invention provides a projection exposure process in which a pattern for transfer which has been formed on the pattern surface of a photomask is illuminated by an exposure beam coming from an illumination optical system and an image of the pattern is formed on a photosensitive substrate via a projection optical system; the process comprising the steps of;
locating the photomask in the optical path extending between the illumination optical system and the projection optical system; and
setting the interval between the pattern surface and the projection optical system at a given value;
the photomask having a transmitting plate having transmission to the exposure beam, disposed apart from the pattern surface by a stated interval; and
the given value being determined in accordance with the thickness of the transmitting plate of the photomask.
Sixteenth invention provides a photomask to be mounted in a projection exposure apparatus with which a pattern for transfer which has been formed on the pattern surface of the photomask is projection-exposed onto a photosensitive substrate by the aid of an exposure beam;
the photomask comprising;
a transmitting plate having transmission to the exposure beam, disposed apart from the pattern surface by a stated interval; and
a mounting surface supported by a mask stage of the projection exposure apparatus;
the mounting surface of the photomask and the pattern surface being set apart by a stated distance in the thickness direction of the transmitting plate;
the stated distance being determined taking account of the thickness of the transmitting plate.
Seventeenth invention provides a photomask to be mounted in a projection exposure apparatus with which a pattern for transfer which has been formed on the pattern surface of the photomask is projection-exposed onto a photosensitive substrate by the aid of an exposure beam;
the photomask comprising;
a transmitting plate having transmission to the exposure beam, disposed apart from the pattern surface by a stated interval;
the transmitting plate being provided with an antireflection coating having a fluoride.
In eighteenth invention, the fluoride may preferably contain at least any one of LaF3 and MgF2.
Nineteen invention provides a projection exposure process comprising the steps of;
illuminating the photomask according to any one of the 7th to 10th, 13th and 16th to 18th invention by the aid of the exposure beam coming from the illumination optical system; and
forming on a photosensitive substrate via the projection optical system an image of a pattern for transfer which has been formed on the photomask.
Twentieth invention provides the photomask according to any one of the 7th to 10th, 13th and 16th to 18th invention, which fulfills at least one condition of the following conditions (axe2x80x2), (bxe2x80x2) and (c).
|xcex94Tcxe2x80x2|xe2x89xa60.1xcex,xe2x80x83xe2x80x83(axe2x80x2)
|xcex94"PHgr"cxe2x80x2|xe2x89xa60.1xcex,xe2x80x83xe2x80x83(bxe2x80x2)
|xcex94n|xc3x97h less than 0.1xcex,xe2x80x83xe2x80x83(c)
where;
xcex: wavelength (m) of the exposure beam;
xcex94Tcxe2x80x2: maximum width (cm) of deviation of the thickness of the transmitting plate from a linear approximation obtained when the thickness is linearly approximated;
xcex94"PHgr"cxe2x80x2: maximum width (cm) of deviation of the isophase plane of plane waves made incident on the transmitting plate and having passed through the transmitting plate, from a linear approximation obtained when the isophase plane is linearly approximated;
xcex94n: difference in refractive index of the transmitting plate with respect to the exposure beam, between its maximum value and its minimum value; and
h: thickness (cm) of the transmitting plate.
Twenty-first invention is that, in a photomask which has a pattern surface where a pattern for transfer has been formed, and is to be irradiated by a stated exposure beam;
the photomask comprises a transmitting plate disposed apart from the pattern surface by a stated interval; and
the transmitting plate fulfills at least one condition of the above conditions (axe2x80x2), (bxe2x80x2) and (c).
Here, the xcex94Tcxe2x80x2 is found in the following way. First, the thickness of the transmitting plate is approximated in a linear line. Next, an absolute value of the maximum width of deviation of an actual thickness of the transmitting plate from the linear line. Then, this absolute value of the maximum width is represented by xcex94Tcxe2x80x2. With regard to the xcex94"PHgr"cxe2x80x2, too, it is similarly found. First the isophase plane of plane waves made incident on the transmitting plate and having passed through the transmitting plate is approximated in a linear line. Then, the absolute value of deviation of the isophase plane from the linear line is represented byxcex94"PHgr"cxe2x80x2.
Twenty-second invention is a process for producing a photomask on which a pattern for transfer is formed and is to be irradiated by a stated exposure beam; the process comprising the steps of;
preparing a transmitting plate having transmission to the exposure beam;
forming on the photomask a pattern for transfer; and
attaching the transmitting plate to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed;
the step of preparing the transmitting plate having an auxiliary step of examining the transmitting plate.
Twenty-third invention is that, in the photomask production process of the 22nd invention, at least one condition of the following conditions (axe2x80x2), (bxe2x80x2) and (c) is examined in the step of preparing the transmitting plate.
|xcex94Tcxe2x80x2|xe2x89xa60.1xcex,xe2x80x83xe2x80x83(axe2x80x2)
|xcex94"PHgr"cxe2x80x2|xe2x89xa60.1xcex,xe2x80x83xe2x80x83(bxe2x80x2)
|xcex94n|xc3x97hxe2x89xa60.1xcex,xe2x80x83xe2x80x83(c)
where;
xcex: wavelength (m) of the exposure beam;
xcex94Tcxe2x80x2: maximum width (cm) of deviation of the thickness of the transmitting plate from a linear approximation obtained when the thickness is linearly approximated;
xcex94"PHgr"cxe2x80x2: maximum width (cm) of deviation of the isophase plane of plane waves made incident on the transmitting plate and having passed through the transmitting plate, from a linear approximation obtained when the isophase plane is linearly approximated;
xcex94n: difference in refractive index of the transmitting plate with respect to the exposure beam, between its maximum value and its minimum value; and
h: thickness (cm) of the transmitting plate.
Twenty-fourth invention is a process for producing a photomask on which a pattern for transfer is formed and is to be irradiated by a stated exposure beam; the process comprising the steps of;
preparing a transmitting plate having transmission to the exposure beam;
forming on the photomask a pattern for transfer; and
attaching the transmitting plate to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed;
the transmitting plate having a stated thickness and has a first surface and a second surface through each of which the exposure beam is to be made to pass;
the first surface and second surface being substantially plane surfaces, or curved surfaces having a stated refracting power, and;
where the angle formed by the first surface and the second surface is represented by xcex8 (unit: degree), the refracting power of the first surface by xcfx861 (unit: 1/mm), and the refracting power of the second surface by xcfx861 (unit: 1/mm);
fulfilling at least one condition of two conditions:
12.4xe2x80x3xe2x89xa6xcex8 less than 3xe2x80x2xe2x80x83xe2x80x83(20),
xe2x88x921/6940 less than xcfx861+xcfx862 less than 1/5,000xe2x80x83xe2x80x83(21),
provided that, when the condition (21) is fulfilled, any one of xcfx861xe2x89xa00 and xcfx862xe2x89xa00 is fulfilled.
Twenty-fifth invention is a process for producing a photomask on which a transfer pattern for transfer is formed and which is to be irradiated by an exposure beam of 200 nm or shorter wavelength; the process comprising the steps of;
preparing a transmitting plate having transmission to the exposure beam;
forming on the photomask a pattern for transfer; and
attaching the transmitting plate to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed;
the process further comprising the step of providing an antireflection coating containing a fluoride.
Twenty-sixth invention is that, in the 25th invention, the fluoride may contain at least any one of LaF3 and MgF2.
Twenty-seventh invention is a process for producing a photomask on which a transfer pattern for transfer is formed and which is to be irradiated by a stated exposure beam; the process comprising the steps of;
preparing a transmitting plate having transmission to the exposure beam;
forming on the photomask a pattern for transfer;
attaching the transmitting plate to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed; and
providing the photomask with a means for changing the position of the pattern for transfer, over the travel direction of the exposure beam.
Twenty-eighth invention is that, in the production process of the 27th invention, the step of providing the photomask with that means comprises an auxiliary step of providing the photomask with a cutout.
Twenty-ninth invention is that, in the production process of the 27th invention, the step of providing the photomask with that means comprises an auxiliary step of providing the photomask with a protrusion.
Thirtieth invention is that, in the production process of the 27th invention, the step of providing the photomask with that means comprises an auxiliary step of preparing a spacer positioned between a stage mounting portion and a stage, of the photomask.
Thirty-first invention is a photomask on which a pattern for transfer is formed in the plane of a pattern surface and which is to be irradiated by a stated exposure beam;
the photomask comprising;
a transmitting plate having a stated thickness and having transmission to the exposure beam; and
a holding member for disposing the transmitting plate apart from the pattern surface by a stated interval;
the holding member holding the transmitting plate in such a way that the angle formed by a light-transmitting surface of the transmitting plate and a surface of the photomask is within 1xc2x0.
Thirty-second invention is that, in the photomask of 31st invention, the holding member holds the transmitting plate in such a way that the angle formed by the light-transmitting surface of the transmitting plate and the surface of the photomask is within 5xe2x80x2.
Thirty-third invention is that, in the photomask of 31st invention, the holding member holds the transmitting plate in such a way that the angle formed by the light-transmitting surface of the transmitting plate and the surface of the photomask is within 1xe2x80x2.
Thirty-fourth invention is a process for producing a photomask on which a transfer pattern for transfer is formed in the plane of a pattern surface and which is to be irradiated by a stated exposure beam; the process comprising the steps of;
preparing a transmitting plate having transmission to the exposure beam;
forming on the photomask a pattern for transfer; and
attaching the transmitting plate to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed;
the step of preparing the transmitting plate being the step of preparing a transmitting plate having a thickness within xc2x12 xcexcm with respect to a specified vale of the thickness of the transmitting plate.
Thirty-fifth invention is that, in the 32nd invention, the step of preparing the transmitting plate has an auxiliary step of examining the transmitting plate; and
in the auxiliary step, the thickness of the transmitting plate is examined.
Thirty-sixth invention is a photomask produced by the production process of the 31st or 32nd invention.
Thirty-seventh invention is a photomask on which a pattern for transfer is formed in the plane of a pattern surface and which is to be irradiated by a stated exposure beam;
the photomask comprising a transmitting plate disposed apart from the pattern surface by a stated interval, having a stated thickness and having a first surface and a second surface through each of which the exposure beam is to be made to pass;
the first surface and second surface standing at a local angle within 0.4xe2x80x3; and
the first and second surfaces and pattern surface standing at a local angle within 12xe2x80x3.
Thirty-eighth invention is a process for producing a photomask on which a transfer pattern for transfer is formed and which is to be irradiated by a stated exposure beam; the process comprising the steps of;
preparing a transmitting plate having transmission to the exposure beam;
forming on the photomask a pattern for transfer; and
attaching the transmitting plate to the photomask in such a way that the transmitting plate stands apart by a stated interval from the surface where the pattern for transfer has been formed;
the transmitting plate having a stated thickness and having a first surface and a second surface through each of which the exposure beam is to be made to pass;
the step of preparing the transmitting plate having an auxiliary step of examining the transmitting plate;
in the auxiliary step, examination being made in relation to a local angle at which the first surface and second surface stand and a local angle at which the first surface and second surface stand with respect to a stated reference surface.
Thirty-ninth invention is that, in the production process of the 36th invention, the first surface and second surface stand at a local angle within 0.4xe2x80x3 and, with respect to a stated reference surface, the first surface and the second surface stand at a local angle within 12xe2x80x3.